APPLICATION OVERVIEW
In most natural gas reserves, the majority of sulfur is present as H2S. However, in some reserves there may be significant concentrations of other sulfur bearing compounds. These “other sulfurs” can generally be divided into four main groups:
- Mercaptans or thiols
- Sulfides
- Disulfides
- Thiophene
There are processes in gas refining facilities designed to remove these other sulfur compounds. Total sulfur measurement is critical in ensuring that processed gas meets contractual pipeline specifications. Typical allowable limits for total sulfur range from 16 to 80 ppm by volume. Total sulfur measurement is further complicated by the issue of gas odorization. Odor is imparted to natural gas in populated areas for safety reasons by the addition of sulfur compounds. Typical odorant compounds are iso-propyl mercaptan, normal-propyl mercaptan, tertiary-butyl mercaptan and thiophene. Total sulfur measurement may be required to balance odor injection levels.
PROTECH903™: AN ECONOMICAL WAY TO MEASURE TRUE TOTAL SULFUR
Galvanic’s ProTech903™ leverages established sensing tape technology for hydrogen sulfide to provide a true total sulfur reading. All sulfur bearing compounds are chemically converted to hydrogen sulfide using hydrogen gas and heat. The resulting hydrogen sulfide is then measured on the sensing tape and reported as total sulfur. There are several analytical methods available that claim to measure total sulfur or selected other sulfur compounds.
A gas chromatograph can be equipped with a Flame Photometric Detector (FPD) which is a type of sulfur specific detector. In this way individual sulfur components can be detected and quantified. However, the chromatographic method detects only a select and finite number of sulfur compounds. In reality a gas sample could contain dozens or hundreds of different sulfur compounds.
ProTech903™ converts all sulfur bearing compounds to H2S, and measures the resulting total as H2S, which provides a true total sulfur measurement. Gas chromatograph techniques are also relatively slow taking 5 – 15 minutes to analyze the sulfur compounds. Protech903™’s built in predictive alarm analyzer provides rapid response to process upsets that can be detected within 20 seconds. FPDs are also complicated to calibrate since they do not generate an equimolar or linear response to sulfur compounds. This means that multiple calibration standards containing multiple sulfur species must be used to calibrate the analyzer. ProTech903™ can be calibrated with a single sulfur compound, such as COS or Methyl Mercaptan, making the calibration and validation process much simpler.
Similarly, spectroscopic techniques can be used to measure sulfur compounds such as hydrogen sulfide, carbonyl sulfide and methyl mercaptan. Again this is a limited and finite number of sulfur compounds that may not represent the true total sulfur content.
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